Optical fiber sensors, per se, are already known. They use a material which, in the presence of moisture, absorbs the moisture and swells, thereby compressing an optical fiber to a greater or lesser extent as a function of the amount of moisture absorbed, which fiber is used for monitoring the connection. The stress applied to the optical fiber gives rise to a local attenuation in transmission and this is detected.
The article entitled "Optical fiber line support system" published in NTT Review, Vol. 3, No. 1, January 1991 describes such a sensor. The optical fiber passes through a mechanical system having a stationary jaw and a moving jaw between which the fiber passes, and having absorbent material that swells in the presence of moisture, thereby optionally actuating the moving jaw. The system applies no stress on the fiber in the absence of any absorbed moisture, and it compresses it with increasing moisture absorption by the material.
That system has the advantage of being particularly simple. However, its reaction time is relatively long and it is not very accurate when it comes to monitoring quickly-varying stresses due to variations in ambient humidity which may be prejudicial to the quality of transmission on the optical line monitored by means of the sensor.
An object of the present invention is to remedy these drawbacks.